The present invention relates to a composition which is capable of imparting non-Newtonian, pseudoplasticity and fluid loss controlling properties to aqueous systems. More particularly, the present invention relates to the formation of a water-based, clay-free, inorganic salt-free and biodegradable drilling fluid for use in drilling horizontal wells for soil and groundwater remediation.
One of the most common methods for subsurface environmental remediation, such as the removal of contaminants from contaminated soil and ground water, is first to bore a wellbore either vertically or horizontally towards the contaminated zone or plume, and then to install an extraction well to extract contaminants using air or fluid to withdraw contaminated ground water. The vertical delivery and recovery systems are by far the most conventional approaches to soil and groundwater remediation. Recent advances in horizontal directional drilling have added a new dimension to the environmental remediation. It is advantageous to drill horizontal wells instead of vertical wells for several reasons. Conventionally drilled vertical wells are perpendicular to the central axis of the contaminated zone, while horizontal wells can travel parallel to such central axis. One horizontal well can treat areas that previously required as many as ten or more vertical wells. The geometry of a horizontal well provides a large well screen area for recovery, thereby improving the efficiency of the remediation process. Moreover, horizontal wells can access areas otherwise inaccessible by vertical wells, such as contaminant sources located underneath buildings, landfills, ponds, and contaminant plumes that have migrated offsite. They thus provide a cost-effective and less destructive method for soil and groundwater remediation.
The purpose of a well drilling method typically is to construct a wellbore that can receive a well casing while causing minimum damage to the formation hosting the well screen. The damage is commonly referred to as skin damage and can be caused by both physical and chemical changes to the host formation. The physical changes generally involve a compacting of the pore spaces and the intrusion of foreign particles into the formation pore spaces. Chemical changes are dissolution and precipitation of minerals caused by any chemical interaction between the formation fluids and the drilling fluid. Skin damage is not strictly limited to the side of the wellbore. The damage continues into the formation as far as the drilling fluid can travel, generally referred to as "invasion". The extent of drilling fluid invasion to the host formation can cause difficulty during well development. Using fluid to aid in drilling often referred to as fluid assisted drilling is the most common and conventional method of horizontal directional drilling (HDD). The principal functions of drilling fluid in HDD include transportation of the drilled soil or rock cuttings to the surface, cooling and cleaning of the drill bit or reamer cutters, reduction of friction between the drill pipe and the wellbore, and borehole stabilization, particularly in soft soil formation, transmission of hydraulic excavation, and soil modification. In addition to performing the functions mentioned above, drilling fluid used in an HDD installation should be environmentally benign and easily processed. A drilling fluid that can be degraded biologically, often referred to as biodegradable, is the most desirable fluid for use in environmental directional well installation.
Generally, drilling fluids will be either clay-based, such as Wyoming bentonite, or clay-free such as brines and polymer slurries. While water is a clay-free fluid, water alone does not have the capacity to carry the drilled cuttings from the borehole to the surface. In the drilling fluid class, clay-based fluids have for years been dominant in the field, because of the traditional and widely held theory that the viscosity suitable for creating a particle carrying capacity in the drilling fluid could be achieved only with a drilling fluid having thixotropic properties, that is, the viscosity must be supplied by a material that will have sufficient gel strength to prevent the drilled particles from separating from the drilling fluid when agitation of the drilling fluid has ceased. In order to obtain the desirable thixotropy or gel strength, hydratable clay or colloidal clay bodies such as sodium-based bentonite have been employed. As a result, the drilling fluids are usually referred to as drilling "muds". The use of drilling muds has provided the means of meeting two basic requirements of drilling fluids, i.e., viscosity for hole cleaning and gel strength for cuttings transportation. However, the clay-based drilling muds form a mud filter cake on the borehole wall which is difficult to remove during well development. Furthermore, the clay particles in the clay-based drilling muds may enter the host formation before a mud cake is formed and formation permeability and porosity may be reduced. When the permeability of a host formation is reduced, the efficiency for withdrawing contaminants from a contaminated soil or groundwater decreases. Yet another serious disadvantage of clay-based drilling muds is that they are not biodegradable and require transportation to a designated area for disposal, thus increasing the cost of the drilling operation.
A non-argillaceous (clay-free) drilling fluid, such as fresh water, avoids many of the clay-based fluid problems, but may cause hydration and disintegration of the host formation. However, fresh water with proper additives may provide a drilling fluid with those basic requirements of drilling fluids. When a clay-free drilling fluid requires relatively high viscosity and gel strength, for example, when used in horizontal directional drilling, it is generally necessary to employ an additive, which may be comprised of a single compound or an admixture of several compounds to thicken the fluid to the point where it will have the necessary carrying capacity and the adequate hole cleaning capability. It is a widely held and accepted theory that a clay-free drilling fluid should exhibit pseudoplastic properties, that is the viscosity must be sufficient to prevent the drilled particles from separating from the drilling fluid when the fluid is under the influence of low shear forces such as those encountered in the annular passage. Materials that can be added to water to create a water-based fluid with pseudoplastic properties are described in the prior art, discussed hereinafter.
Another requirement of a drilling fluid for boring a hole, either vertically or directionally, is a low fluid loss or filtration rate as commonly referred to in the oil and gas well drilling art. It is not enough that a drilling fluid has adequate viscosity and gel strength to prevent the drilled cuttings from settling when circulation of the fluid is stopped. If the drilling fluid does not have a low filter loss, it may result in loss of the drilling fluid to the host formation, particularly when drilled through an unconsolidated formation such as sandy soil. In the article entitled "Fluids Are Key in Drilling Highly Deviated Wells," published in Petroleum Engineer International, Feb. 1988 (pp. 24-26), B. Byrd and M. Zamora described the importance of filtration control to minimize formation damage in drilling highly deviated wells. A drilling fluid with a low filtration rate allows only a small amount of water to diffuse from the drilling fluid to the formation surrounding the wellbore under the pressure differential prevailing in the borehole.
U.S. Pat. No. 4,240,915 to Block discloses a water-based, clay-free drilling fluid suitable for circulating in a borehole while drilling the borehole into a subterranean formation, such fluid including water, a water loss inhibitor, a weighing agent and a viscosifying agent, in which the viscosifying agent is an aqueous medium produced by mixing under a high degree of agitation a water soluble alkali metal aluminate (Na.sub.2 O.circle-solid.Al.sub.2 O.sub.3 .circle-solid.3H.sub.2 O) with a water soluble acidic compound selected from the group consisting of an inorganic acid or a salt of a strong acid and a weak base. The aqueous part of the drilling fluid has the aluminum hydroxide agent in an amount sufficient to impart non-Newtonian, pseudoplastic properties to the fluids when the fluids have a pH of at least 8.
U.S. Pat. No. 4,255,268 to Block discloses a water-based, clay-free drilling fluid for use in drilling boreholes into subterranean formations having an aqueous mixture of water, a water-loss inhibitor, a weighting agent and a viscosifying agent, in which the viscosifying agent is a ferric hydroxide reaction product formed in an aqueous media by contacting under a high degree of agitation a water soluble ferric salt such as ferric chloride (FeCl.sub.3) with a water soluble base which contains or produces hydroxide groups in water in amounts to cause the hydroxy to ferric ratio to be at least about 3:1, for example Fe(OH).sub.3. The aqueous phase of the drilling fluid has the ferric hydroxide Fe(OH),! agent therein in an amount sufficient to impart non-Newtonian, pseudoplastic properties to the fluid at a pH of at least 8.
U.S. Pat. No. 4,264,455 to Block is directed to an aqueous, clay-free drilling fluid for use in drilling boreholes into subterranean formations having an aqueous system comprising water, a water-loss inhibitor, and a viscosifying agent, in which the viscosifying agent is a hydroxyl containing magnesium containing reaction product. The hydroxyl containing magnesium agent of the reaction product is formed in an aqueous medium under high speed agitation between a magnesium salt, such as MgO, which is substantially soluble in water and a water soluble base selected from the group consisting of alkali metal oxide, alkali metal hydroxide, alkali metal salt of a weak acid and ammonium hydroxide. The aqueous system of the drilling fluid has the subject reaction product therein in an amount sufficient to impart non-Newtonian, pseudoplastic properties to the fluids when the fluids have a pH above 11.
U.S. Pat. No. 4,366,070 to Block describes an improved water-based, clay-free drilling fluid that is capable of imparting a high degree of pseudoplastic and fluid loss controlling properties. The composition is a combination of a hydroxy containing aluminum agent having an assumed molecular formula of AlO(OH) and a cross-linked hydroxyalkyl cellulose reaction product. The composition involves (1) a hydroxy containing aluminum agent formed by mixing in an aqueous solution and under high degree of agitation a water soluble basic agent selected from an alkali metal aluminate, alkali metal hydroxide or ammonium hydroxide with a water soluble acidic agent selected from an inorganic acid, or aluminum chloride, sulfate or nitrate such that at least one of such agents is an aluminum containing compound; (2) a reaction product formed between a hydroxyalkyl cellulose and a cross-linking agent, the cross-linking agent being present at a concentration equivalent to at least about 1% of stoichiometry with respect to the hydroxyalkyl cellulose.
U.S. Pat. No. 4,428,845 to Block is directed to a composition for imparting both pseudoplasticity and water loss control to alkaline aqueous systems and to the use of such compositions to form an improved water-based, clay-free drilling fluid. The composition is a combination of (1) a hydroxy containing aluminum agent similar to that described in the U.S. Pat. No. 4,366,070; and (2) a reaction product formed in an acidic medium between a polyvinyl alcohol with 0.01 to 0.1% of stoichiometry of a polyaldehyde. Both polyvinyl alcohol and polyaldehyde are synthetic (man-made) polymers, as opposed to naturally occurring polymers.
U.S. Pat. No. 4,473,479 to Block describes a composition that is capable of imparting a high degree of pseudoplastic and water loss controlling properties to aqueous systems and to the use of such compositions to form an improved water-based, clay-free drilling fluid. The subject composition is a combination of a hydroxy containing aluminum agent similar to the one described in the U.S. Pat. Nos. 4,428,845 and 4,366,070, and a reaction product formed between a hydroxyalkyl and a cross-linking agent. The cross-linked hydroxyalkyl cellulose reaction product is similar to the one described in the U.S. Pat. No. 4,366,070.
U.S. Pat. No. 3,988,246 to Hartfiel is directed to an improved clay-free wellbore fluid having thixotropic gel properties for use in subterranean formations, in which the fluid includes water, a viscosifying amount of a heteropolysaccharide produced by the action of bacteria of the genus Xanthomonas on carbohydrates, a stabilizing amount of magnesium oxide (MgO), an organic starch derivative and a brine forming soluble salt. In some situations a salt of lignosulfonate is added to maintain the desirable properties of wellbore fluid.
U.S. Pat. Nos. 4,025,443 and 4,151,096 to Jackson each describes an additive composition for use in clay-free, non-argillaceous, wellbore fluids including a hydroxyalkyl guar gum and a stabilizing amount of magnesia and a highly infusible magnesium oxide (MgO), or magnesium hydroxide Mg(OH).sub.2 !. One theory of the effectiveness of these two patents is that the very slightly soluble magnesia which is present in excess of its solubility in the wellbore fluid provides a reservoir of basicity of just the correct amount to maintain the Ph of the fluid in the range at which the guar gum is most stable. Without the addition of magnesia or magnesium hydroxide, guar gum, which is well known to be unstable or degradable in neutral pH environment, deteriorates rapidly.
U.S. Pat. No. 4,422,947 to Dorsey et al is directed to a clay-based or clay-free aqueous thixotropic wellbore fluid having improved fluid loss control, desirable flow characteristics and low shale sensitivity for use in drilling a well. The fluid includes water or a brine base including an effective amount of an additive including (1) a cross-linked potato starch, heteropolysaccharide cross-linked with a cross-ling compound selected from either phosphorous oxychloride or urea-formaldehyde, (2) a heteropolysaccharide derived from a carbohydrate by bacteria of the genus Xanthomonas, and (3) a hydroxyethylcellulose. Such a wellbore fluid is either clay-based, or a clay-free but is a brine-based solution containing water soluble salts such as sodium chloride (NaCl), calcium chloride (CaCl) or potassium chloride (KC1). This patent is also directed to a liquid concentrate water loss control additive for use in water-based or brine-based wellbore fluids with the same composition as that in the dry mix additive described previously. However, the liquid concentrate additive according to this patent contemplates the carrier being either an alcohol or diesel oil.
U.S. Pat. No. 5,407,909 to Goodhue, Jr. et. al is directed to a method for preparing and using an earth stabilization fluid comprising (1) adding water into an earth cavity, (2) adding dry powder PHPA into the cavity; and (3) excavating to enlarge the cavity while a portion of the dry powder PHPA is in a transitory, partially hydrated swollen state.
In summary, the patents of Block, as described above, involve a water-based, clay-free drilling fluid for use in drilling boreholes into subterranean formations having an aqueous mixture consisting of water, a water loss inhibition and a viscosifying agent. The viscosifying agent disclosed in each such patent to Block involves an inorganic compound, for example, aluminum hydroxide in U.S. Pat. No. 4,240,915, ferric hydroxide in U.S. Pat. No. 4,255,268, magnesium hydroxide in U.S. Pat. No. 4,264,455, and hydroxy containing aluminum in each of U.S. Pat. Nos. 4,366,070; 4,428,845; and 4,473,479. Those inorganic viscosifying agents are not biodegradable and some of them are not completely soluble in water. The insoluble particles or fines in the clay-free but not solid-free water-based drilling fluid can block or restrict flow through the host formations, thus reducing the efficiency of environmental remediation involving the withdrawal of the contaminated groundwater from subterranean formations. The water-based, clay-free drilling fluids described in such patents to Block simply are not environmentally acceptable for use in environmental horizontal well installation for soil and groundwater remediation.
Also in summary, the patents of Hartfiel and Jackson, described above, involve viscosifying agents derived from heteropolysaccharides, for example, a heteropolysaccharide produced from carbohydrates with Xanthomonas bacteria in U.S. Pat. No. 3,988,246 (to Hartfiel), hydroxyalkyl guar gum in U.S. Pat. Nos. 4,025,443 and 4,151,096 (both to Jackson); however, none of those viscosifying agents are stable without the addition of a magnesium containing inorganic compound. The clay-free wellbore fluids of Hartfiel and Jackson are likewise not suitable for environmental horizontal well installation applications.
A heteropolysaccharide cross-linked with phosphorous oxychloride and urea-formaldehyde is employed as the viscosifying agent in the above-noted patent to Dorsey et. al. Urea-formaldehyde and its derivatives are known to be environmentally unfriendly substances. Furthermore, the dry additive in this patent was intended to be used in a brine-based completion fluid for oil/gas well drilling and completion works, in which the liquid concentrate is dispersed or suspended in alcohol or diesel oil, neither of which is suitable for use in environmental horizontal directional drilling such as environmental well installation.
A high molecular weight, synthetic copolymer of polyacrylamide and polyacrylate when mixed with fresh water provides a viscous polymer solution for use in geoconstruction drilling such as drilled shaft and trenching. This type of clay-free, borehole stabilizing fluid described in the prior art to Goodhue Jr. et. al does not exhibit those prerequisite properties of a drilling fluid such as pseudoplasticity and gel strength for cuttings suspension and low fluid loss control capability. The fluid mentioned in this patent provides only fluid viscosity and cohesion to keep the drilled borehole from sloughing. Without any exception, the patent to Goodhue et al is only applicable to bore vertical holes with a limited depth of perhaps 250 feet. The fluid described in U.S. Pat. No. 5,407,909 simply is not suitable for boring a far reached directional particularly horizontal borehole. Moreover, the copolymer of polyacrylamide and polyacrylate is not considered to be a biodegradable polymer. The copolymer, which forms a hydrated, deformed mass in water, adsorbs tightly on the surface of the formation and coats or encapsulates the formation particles. The encapsulation may cause disruption of flow of the host formation. As the result, such a fluid is not suitable for use in environmental horizontal well installation for soil and groundwater remediation.
It is therefore the primary object of the present invention to provide an aqueous, clay-free and inorganic salt-free, pseudoplastic, stable drilling fluid which does not damage the formations hosting the borehole.
It is also an object of the present invention to form an aqueous, clay-free, inorganic salt-free, and biodegradable fluid which exhibits non-Newtonian, pseudoplastic properties so as to be capable of drilling boreholes, particularly directional or horizontal boreholes, and the like in an efficient manner.
Further, it is the object of the present invention to form a drilling fluid which is substantially stable to varying environmental conditions of low pH normally encountered in borehole drilling.
Yet, it is another object of the present invention to form a drilling fluid which is biodegradable, which does not damage the host formations surrounding the drilled borehole, which does not block the passage or flow path of the formations.
Still, it is the object of the present invention to form a drilling fluid which exhibits low fluid loss and high gel strength properties so as to be capable of drilling boreholes in an unconsolidated formation.
It is also an object of the present invention to provide a drilling fluid additive consisting of a dry mixture of a naturally occurring polymer and a biopolymer. When such dry mixture additive is mixed with an aqueous continuous phase including fresh water and/or acidic water with a low pH, it provides a homogeneous drilling fluid having sufficient, stable viscosity for hole cleaning, adequate gel strength, particularly initial gel strength for cuttings or spoils suspension, and low water loss control, a most desirable fluid property when drilling in an unconsolidated formations such as sandy soil.
It is an additional advantage of the present invention that the drilling fluid formulated with the dry concentrate comprising an admixture of polymers is non-toxic, and biodegradable.
It is a further advantage of the present invention that this water-based, clay-free, biodegradable, pseudoplastic drilling fluid is most suitable for drilling environmental horizontal wells for remediation works.
These and other advantages and features of the present invention will become apparent from a reading as the following disclosure, description and teachings set out below.